The present invention is directed to precision casting wherein an investment mold is formed from an expendible pattern.
Precision casting or molding is employed to form products which generally require minimal final finishing. Such castings are well-known in the precision arts such as precision engineering, clock work, dental and precious metal ornamentations. A wax-like expendible pattern is made directly or from the master mold. The expendible pattern is then encased in a wet slurry or paste consisting of a suitable fine grain refractory mold material and a bonding agent such as a plaster of paris. The coating closely envelops the expendible pattern reproducing essentially each and every detail of its shape and configuration. The mold material is solidified to form a mold or investment with the pattern invested in place. The investment is then heated or otherwise treated to remove the expendible pattern and to define a hard and strong mold. The final cast product is immediately formed while the investment is hot by introduction of the metal into the mold and filling the mold. Generally, under the broad field of investment molding, the metal may be introduced under gravity pressure and even in some cases under centrifugal means. Finally when the metal has solidified, the mold is removed or broken away, leaving the final product with the highly finished surface.
The investment casting may advantageously employ a vacuum chamber within which the mold is located during the filling of the expendible mold. Various vacuum systems have been suggested wherein a suitable cup-shaped enclosure is provided within which the expendible porous investment is placed. A relatively high vacuum pump is coupled to the chamber to establish the usual relatively high pressure vacuum on the order of barometric pressure and with a minimum of air flow. For example, U.S. Pat. No. 3,780,781 which issued Dec. 25, 1973, discloses an investment casting system wherein a porous mold is formed in accordance with any conventional practice and then placed within special enclosure with an automatic upper sealing wall to define a relatively closed encircling vacuum chamber. The chamber is connected to the conventional vacuum pump source widely employed in vacuum investment casting. With the heat investment located within the chamber, the vacuum pump is operated to draw a full vacuum after which the casting material is introduced into the mold.
Although such special apparatus has been widely employed in precision casting, there is a significant need for a simple, reliable investment casting apparatus which can be employed in the home, school and small business to permit forming of precious metal ornaments, dental bridges, crowns and the like as well as the hobbyist for making small cast objects such as gears or inexpensive ornaments.